Lithium Ion Battery Binder Observations and Measurements of Physical Properties in Electrolyte Solution Using Scanning Probe Microscopy (SPM)

Introduction

Lithium (Li) ion batteries are used widely as rechargeable batteries in small electronic appliances such as digital cameras and mobile phones. Lithium ion batteries are also being developed for use in hybrid cars and electric vehicles, and further improvements are expected in terms of increased power output and battery performance. Lithium ion batteries are composed of a cathode, anode, separator and electrolyte, where the active material that comprises the cathode and anode are retained in place by the binder. Normally the anode is made from a graphite active material, but recent years have seen research into silicon (Si) active materials as next-generation anode materials that will have a higher theoretical capacity than graphite active materials. Since Si anode active materials expand and contract substantially during charge and discharge as a result of incorporation and loss of Li ions, use of an Si active material for the anode makes the battery prone to breakage on repeated charge/discharge cycles and a short lifespan. To compensate for this issue, it is important to use a hard binder that is spread evenly in the battery to securely bind and retain the active material. Here, we carried out SPM shape observations of binder samples held in both the electrolyte material used for actual battery operation and in N₂ gas for reference. The physical properties of binder samples were also measured in electrolyte to find the binder most suited to use in batteries with an Si active material as the anode.

November 13, 2013 GMT